All approaches to starlight suppression are subject to spectral bandpass limitations. For nulling interferometers (“nullers”), the issue lies in achieving broadband symmetry between destructively interfering beams. In this effort we propose to improve upon the use of Fresnel rhombs as achromatic phase shifters (APS) for broadband high contrast nulling interferometry by adding dielectric coatings to each rhomb. These components will be characterized along with a fiber bundle spatial filter array (SFA) that is used for complex wavefront control. These components (the APS and SFA) are used in parallel to ultimately reach contrasts needed for Earth-like exoplanet detection.

The objectives of this project include 1) designing and tolerancing a new set of coated Fresnel rhomb APS that will, in theory, improve broadband peformance by over two orders of magnitude compared to a previous generation set of APS, 2) procuring one or more symmetric sets of APS and fabricating new mounting hardware, and 3) measuring and verifying the performance of the APS. The end goal or product is to produce an enhanced set of optics that improve the performance of the current, uncoated APS rhombs by two to three orders of magnitude, for use in testing with future demonstrations of the Segmented Aperture Interferometric Nulling Testbed (SAINT), which uses the Visible Nulling Coronagraph (VNC) for high-contrast source suppression. This is a technology maturation effort for missions such as the Habitable Exoplanet Imager (HabEx) or a future large aperture UV/Optical/IR telescope (LUVOIR) Surveyor. The innovative elements include a fabrication scheme that yields symmetric optics, and a test regiment that can measure prism angles with sub-arcsecond precision and retardance to micro-radian precision.",
"technologyMaturityCurrent": 3,
"title": "Broadband Phase Shifter for High Contrast Nulling Interferometry",
"leadOrganization": {
"acronym": "GSFC",
"city": "Greenbelt",
"name": "Goddard Space Flight Center",
"state": "MD",
"type": "NASA Center"
},
"technologyMaturityEnd": 4,
"additionalTas": "",
"principalInvestigators": {"principalInvestigator": "Matthew R Bolcar"},
"lastUpdated": "2017-12-04",
"library": {"libraryItem": {
"description": "Shown here are the previous generation uncoated retardance curves, along with the new coated APS retardance curve that in theory achieves greater than two orders of magnitude improved performance.",
"files": {"file": {
"size": 302642,
"id": 26333,
"url": "https://techport.nasa.gov/file/26333"
}},
"id": 35344,
"title": "Achromatic Phase Shifter for Visible Nulling Coronagraphs",
"type": "Image"
}},
"technologyMaturityStart": 3,
"responsibleMissionDirectorateOrOffice": "Mission Support Directorate",
"id": 90760,
"startDate": "Oct 2016",
"status": "Completed"
}}